1. Field of the Invention
The present invention relates to a fluid-filled vibration damping device which exhibits a vibration damping effect based on flows of a non-compressible fluid enclosed therein, and which are particularly suitable for use as, e.g., automotive-vehicle engine mounts, body mounts, and differential mounts.
2. Related Art Statement
There is known a fluid-filled vibration damping device as a sort of vibration-damping connecting or supporting device that is interposed between two members of a vibration transmitting system, for connecting the two members in a vibration damping fashion. The fluid-filled vibration damping device includes a first mounting member adapted to be attached to one of the two members; a second mounting member adapted to be attached to the other of the two members; and an elastic rubber body which elastically connects the first and second mounting members to each other and which provides a portion of a fluid-chamber wall defining a fluid chamber filled with a non-compressible fluid. When a vibrational load is applied to the vibration damping device, it exhibits a vibration damping effect based on flows of the fluid in the fluid chamber, in particular, resonance of the fluid.
Meanwhile, there has been proposed another fluid-filled vibration damping device which includes, in addition to the above-indicated members, a working or umbrella-shaped member which is supported by the first mounting member such that the umbrella member extends, in the fluid chamber, in a direction substantially perpendicular to a direction in which a main vibrational load is applied to the vibration damping device, and thereby divides the fluid chamber into two divided chambers which are located on opposite sides of the umbrella member, respectively, and which are communicated with each other via a fluid-flow restricting passage defined by at least the umbrella member.
Upon application of the main vibrational load to the second vibration damping device including the umbrella member, the umbrella member is reciprocatively moved in the fluid chamber, so that the fluid flows through the fluid-flow restricting passage. The second vibration damping device can exhibit a vibration damping effect based on the flows of the fluid through the restricting passage, in particular, the resonance of the fluid.
However, even in the second vibration damping device, the vibration damping effect based on the flows of the fluid through the restricting passage defined by the umbrella member is effective against only vibrations having frequencies in a pre-tuned frequency range. In particular, when a vibration having a frequency higher than the pre-tuned range is input to the vibration damping device, the resistance to the flows of the fluid through the restricting passage is excessively increased so that the vibration damping device exhibits an inappropriate (i.e., high) dynamic spring characteristic, which leads to largely lowering the vibration damping performance of the device. Thus, the prior vibration damping device cannot exhibit an appropriate or low dynamic spring characteristic in a wide frequency range.